Windows XP (codenamed Whistler)[5] is a personal computeroperating system produced by Microsoft as part of the Windows NT family of operating systems. The operating system was released to manufacturing on August 24, 2001, and generally released for retail sale on October 25, 2001.

Development of XP began in the late 1990s as "Neptune", an operating system built on the Windows NT kernel which was intended specifically for mainstream consumer use—an updated version of Windows 2000 was also originally planned for the business market. However, in January 2000, both projects were shelved in favor of a single OS codenamed "Whistler", which would serve as a single OS platform for both consumer and business markets. Windows XP was a major advance from the MS-DOS based versions of Windows in security, stability and efficiency[6] due to its use of Windows NT underpinnings. It introduced a significantly redesigned graphical user interface and was the first version of Windows to use product activation in an effort to reduce software piracy.

Upon its release Windows XP received generally positive reviews, with critics noting increased performance (especially in comparison to Windows ME), a more intuitive user interface, improved hardware support, and its expanded multimedia capabilities.[7] Despite some initial concerns over the new licensing model and product activation system, Windows XP eventually proved to be popular and widely used. It is estimated that at least 400 million copies of Windows XP were sold globally within its first five years of availability,[8][9] and at least one billion copies were sold by April 2014.[10]

Windows XP remained popular even after the release of newer versions, particularly due to the poorly received release of its successor Windows Vista. Vista's 2009 successor, Windows 7, only overtook XP in total market share at the end of 2011.

In the late 1990s, initial development of what would become Windows XP was focused on two individual products; "Odyssey", which was reportedly intended to succeed the future Windows 2000, and "Neptune", which was intended to succeed the MS-DOS-based Windows 98 with a Windows NT-based product designed for consumers. Based on 2000's NT 5.0 kernel, Neptune primarily focused on offering a simplified, task-based interface based around a concept known internally as "activity centers". A number of activity centers were planned, serving as hubs for communications (i.e. email), playing music, managing or viewing photos, searching the internet, and viewing recently used content. A single build of Neptune, 5111 (which was otherwise based on, and still carried the branding of Windows 2000 in places), revealed early work on the activity center concept, with an updated user account interface and graphical login screen, common functions (such as recently used programs) being accessible from a customizable "Starting Places" page (which could be used as either a separate window, or a full-screen desktop replacement).[11][12][13]

However, the project, at its current state, proved to be too ambitious. Microsoft would ultimately shelve Bill Gates' 1998 promise that Windows 98 would be the final MS-DOS based version of Windows; at the WinHEC conference on April 7, 1999, Steve Ballmer announced an updated version of 98 known as Windows Millennium. Microsoft also planned to push back Neptune in favor of an interim, but consumer-oriented NT-based OS codenamed "Asteroid". Concepts introduced by Neptune would influence future Windows products; in Windows ME, the activity center concept was used for System Restore and Help and Support (which both combined Win32 code with an interface rendered using Internet Explorer's layout engine), the hub concept would be expanded on Windows Phone, and Windows 8 would similarly use a simplified user interface running atop the existing Windows shell.[14][15]

In January 2000, shortly prior to the official release of Windows 2000, technology writer Paul Thurrott reported that Microsoft had shelved both Neptune and Odyssey in favor of a new product codenamed Whistler, after Whistler, British Columbia, as many Microsoft employees skied at the Whistler-Blackcomb ski resort.[5] The goal of Whistler was to unify both the consumer and business-oriented Windows lines under a single, Windows NT platform, further stating that: "Neptune became a black hole when all the features that were cut from [Windows ME] were simply re-tagged as Neptune features. And since Neptune and Odyssey would be based on the same code-base anyway, it made sense to combine them into a single project".[13] At WinHEC in April 2000, Microsoft officially announced and presented an early build of Whistler, focusing on a new modularized architecture, built-in CD burning, fast user switching, and updated versions of the digital media features introduced by ME. Windows general manager Carl Stork stated that Whistler would be released in both consumer- and business-oriented versions built atop the same architecture, and that there were plans to update the Windows interface to make it "warmer and more friendly".[11][13]

In June 2000, Microsoft began the technical beta testing process; Whistler was expected to be made available in "Personal", "Professional", "Server", "Advanced Server", and "Datacenter" editions. At PDC on July 13, 2000, Microsoft announced that Whistler would be released during the second half of 2001, and also released the first preview build, 2250. The build notably introduced an early version of a new visual styles system along with an interim theme known as "Professional" (later renamed "Watercolor"), and contained a hidden "Start page" (a full-screen page similar to Neptune's "Starting Places"), and a hidden, early version of a two-column Start menu design.[16] Build 2257 featured further refinements to the Watercolor theme, along with the official introduction of the two-column Start menu, and the addition of an early version of Windows Firewall.[13]

Microsoft released Whistler Beta 1, build 2296, on October 31, 2000. Build 2410 in January 2001 introduced Internet Explorer 6.0 (previously branded as 5.6) and the Windows Product Activation system. Bill Gates dedicated a portion of his keynote at Consumer Electronics Show to discuss Whistler, explaining that the OS would bring "[the] dependability of our highest end corporate desktop, and total dependability, to the home", but also "move it in the direction of making it very consumer-oriented. Making it very friendly for the home user to use." Alongside Beta 1, it was also announced that Microsoft would prioritize the release of the consumer-oriented versions of Whistler over the server-oriented versions in order to gauge reaction, but that they would be both generally available during the second half of 2001 (Whistler Server would ultimately be delayed into 2003).[17] Builds 2416 and 2419 added the File and Transfer Settings Wizard and began to introduce elements of the operating system's final appearance (such as its near-final Windows Setup design, and the addition of new default wallpapers, such as Bliss).[18]

On February 5, 2001, Microsoft officially announced that Whistler would be known as Windows XP, short for "experience". As a complement, the next version of Microsoft Office was also announced as Office XP. Microsoft stated that the name "[symbolizes] the rich and extended user experiences Windows and Office can offer by embracing Web services that span a broad range of devices." In a press event at EMP Museum in Seattle on February 13, 2001, Microsoft publicly unveiled the new "Luna" user interface of Windows XP. Windows XP Beta 2, build 2462a (which among other improvements, introduced the Luna style), was launched at WinHEC on March 25, 2001.[19][20]

In April 2001, Microsoft controversially announced that XP would not integrate support for Bluetooth or USB 2.0 on launch, requiring the use of third-party drivers. Critics felt that in the case of the latter, Microsoft's decision had delivered a potential blow to the adoption of USB 2.0, as XP was to provide support for the competing, Apple-developed FireWire standard instead. A representative stated that the company had "[recognized] the importance of USB 2.0 as a newly emerging standard and is evaluating the best mechanism for making it available to Windows XP users after the initial release."[21] The builds prior to and following Release Candidate 1 (build 2505), released on July 5, 2001, and Release Candidate 2 (build 2526, released on July 27, 2001), focused on fixing bugs, acknowledging user feedback, and other final tweaks before the RTM build.[20]

On August 24, 2001, Windows XP build 2600 was released to manufacturing. During a ceremonial media event at Microsoft Redmond Campus, copies of the RTM build were given to representatives of several major PC manufacturers in briefcases, who then flew off on XP-branded helicopters. While PC manufacturers would be able to release devices running XP beginning on September 24, 2001, XP was expected to reach general, retail availability on October 25, 2001. On the same day, Microsoft also announced the final retail pricing of XP's two main editions, "Home" and "Professional".[20][22]

In June 2001, Microsoft indicated that it was planning to, in conjunction with Intel and other PC makers, spend at least US$1 billion on marketing and promoting Windows XP, among these efforts included a U.S. television commercial featuring Madonna's song "Ray of Light".[23][24]

While retaining some similarities to previous versions, Windows XP's interface was overhauled with a new visual appearance, with an increased use of alpha compositing effects, drop shadows, and "visual styles", which completely change the appearance of the operating system. The amount of effects enabled are determined by the operating system by the computer's processing power, and can be enabled or disabled on a case-by-case basis. XP also added ClearType, a new subpixel rendering system designed to improve the appearance of fonts on LCD displays.[25] A new set of system icons were also introduced.[26][27] The default wallpaper, Bliss, is a photo of a landscape in the Napa Valley outside Napa, California, with rolling green hills and a blue sky with stratocumulus and cirrus clouds.[28]

The Start menu received its first major overhaul on XP, switching to a two-column layout with the ability to list, pin, and display frequently used applications, recently opened documents, and the traditional cascading "All Programs" menu. The taskbar can now group windows opened by a single application into one taskbar button, with a popup menu listing the individual windows. The notification area also hides "inactive" icons by default. The taskbar can also be "locked" to prevent accidental moving or other changes. A "common tasks" list was added Windows Explorer's sidebar was updated to use a new task-based designs with lists of common actions; the tasks displayed are contextually relevant to the type of content in a folder (i.e. a folder with music displays offers to play all the files in the folder, or burn them to a CD).

Fast user switching allows additional users to log into a Windows XP machine without existing users having to close their programs and logging out. Although only one user at the time can use the console (i.e. monitor, keyboard and mouse), previous users can resume their session once they regained control of the console.[29]

In an effort to prevent software piracy, XP also introduced Windows Product Activation, which requires that each Windows license be "activated" and tied to a unique ID generated using information from the computer hardware.

Windows XP uses prefetcher to improve startup and application launch times.[30][31] It also became possible to revert the installation of an updated device driver, should one not produce desirable results.[32]

Diagram representing the main editions of Windows XP. It is based on the category of the edition (grey) and codebase (black arrow).

Windows XP was released in two major editions on launch; Home Edition, and Professional. Both editions were made available at retail as pre-loaded software on new computers, and in boxed copies. Boxed copies were sold as "Upgrade" or "Full" licenses; the "Upgrade" versions were slightly cheaper, but require an existing version of Windows to install. The "Full" version could be installed on systems without an operating system or existing version of Windows.[24] Both versions of XP were aimed towards different markets; Home Edition is explicitly intended for consumer use and disables or removes certain advanced and enterprise-oriented features present on Professional, such as the ability to join a Windows domain, Internet Information Services, and Multilingual User Interface. Additionally, users could not directly upgrade to XP Home Edition from Windows NT 4.0 or 2000, although users could upgrade to either variant of XP from Windows 98 or ME.[38] Windows' software license agreement for pre-loaded licenses allows the software to be "returned" to the OEM for a refund if the user does not wish to use it.[39] Despite the refusal of some manufacturers to honor the entitlement, it has been enforced by courts in some countries.[40][41]

Microsoft also targeted emerging markets with the 2004 introduction of Windows XP Starter Edition, a special variant of Home Edition intended for low-cost PC's. The OS is primarily aimed at first-time computer owners (particularly in developing countries); containing heavy localization (including wallpapers and screen savers incorporating images of local landmarks), and a "My Support" area which contains video tutorials on basic computing tasks. It also removes certain "complex" features, and does not allow users to run more than three applications at a time. After a pilot program in India and Thailand, Starter was released in other emerging markets throughout 2005.[45] In 2006, Microsoft also unveiled the FlexGo initiative, which would also target emerging markets with subsidized PCs on a pre-paid, subscription basis.[46]

As the result of unfair competition lawsuits in Europe and South Korea, which both alleged that Microsoft had improperly leveraged its status in the PC market to favor its own software, Microsoft was forced to release special versions of XP in these markets that excluded certain applications. In March 2004, after the European Commissionfined Microsoft €497 million (US$603 million), Microsoft was forced to release "N" versions of XP that excluded Windows Media Player, encouraging users to pick and download their own media player software. As it is sold at the same price as the version with Windows Media Player included, certain OEMs (such as Dell, who offered it for a short period, along with Hewlett-Packard, Lenovo and Fujitsu Siemens) chose not to offer it. Consumer interest has been low, with roughly 1,500 units shipped to OEMs, and no reported sales to consumers.[47][48][49][50] In December 2005, the Korean Fair Trade Commission ordered Microsoft to make available editions of Windows XP and Windows Server 2003 that do not contain Windows Media Player or Windows Messenger.[51] The "K" and "KN" editions of Windows XP were released in August 2006, and are only available in English and Korean, and also contain links to third-party instant messenger and media player software.[52]

Three service packs were released for Windows XP, containing various bug fixes and the addition of certain features. Each service pack is a superset of all previous service packs and patches so that only the latest service pack needs to be installed, and also includes new revisions.[53]

Service Pack 1 (SP1) for Windows XP was released on September 9, 2002. It contained over 300 minor, post-RTM bug fixes, along with all security patches released since the original release of XP. SP1 also added USB 2.0 support, Microsoft Java Virtual Machine, .NET Framework support, and support for technologies used by the then-upcoming Media Center and Tablet PC editions of XP. The most significant change on SP1 was the addition of Set Program Access and Defaults, a settings page which allows users and OEMs to set default programs for certain types of activities (such as media players or web browsers) and disable access to bundled, Microsoft programs (such as Internet Explorer or Windows Media Player). This was added as part of the company's settlement in United States v. Microsoft Corp., which stated that Microsoft would allow users to "enable or remove access to each Microsoft Middleware Product or Non-Microsoft Middleware Product by displaying or removing icons, shortcuts, or menu entries on the desktop or Start menu, or anywhere else in a Windows Operating System Product where a list of icons, shortcuts, or menu entries for applications are generally displayed."[54][55][56]

On February 3, 2003, Microsoft released Service Pack 1a (SP1a). This release removed Microsoft Java Virtual Machine as a result of a lawsuit with Sun Microsystems.[57]

Service Pack 2 (SP2) was released on August 25, 2004,[58] SP2 added new functionality to Windows XP, such as WPA encryption compatibility and improved Wi-Fi support (with a wizard utility), a pop-up ad blocker for Internet Explorer 6, and partial Bluetooth support.

Service Pack 2 also added new security enhancements (codenamed "Springboard"),[59] which included a major revision to the included firewall (renamed Windows Firewall, and now enabled by default), Data Execution Prevention gained hardware support in the NX bit that can stop some forms of buffer overflow attacks. Raw socket support is removed (which supposedly limits the damage done by zombie machines) and the Windows Messenger service became disabled by default, which was an attack vector for pop-up advertisements to be displayed as system messages without a web browser or any additional software. Additionally, security-related improvements were made to e-mail and web browsing. Service Pack 2 also added Security Center, an interface which provides a general overview of the system's security status, including the state of the firewall and automatic updates. Third-party firewall and antivirus software can also be monitored from Security Center.[60]

In August 2006, Microsoft released updated installation media for Windows XP and Windows Server 2003 SP2 (SP2b) to contain a patch that requires ActiveX controls to require manual activation in accordance with a patent held by Eolas.[61][62] Microsoft has since licensed the patent, and released a patch reverting the change in April 2008.[63] In September 2007, another minor revision known as SP2c was released for XP Professional, extending the number of available product keys for the operating system to "support the continued availability of Windows XP Professional through the scheduled system builder channel end-of-life (EOL) date of January 31, 2009."[64]

Windows XP Service Pack 3 (SP3) was released to manufacturing on April 21, 2008, and to the public via both the Microsoft Download Center and Windows Update on May 6, 2008.[65][66][67][68]

It began being automatically pushed out to Automatic Updates users on July 10, 2008.[69] A feature set overview which details new features available separately as stand-alone updates to Windows XP, as well as backported features from Windows Vista, has been posted by Microsoft.[70] A total of 1,174 fixes have been included in SP3.[71] Service Pack 3 can be installed on systems with Internet Explorer versions 6, 7, or 8.[72] Internet Explorer 7 and 8 are not included as part of SP3.[73] Service Pack 3 is not available for the 64 bit version of Windows XP, which is based on Windows Server 2003 kernel.

Service Pack 3 contains updates to the operating system components of Windows XP Media Center Edition (MCE) and Windows XP Tablet PC Edition, and security updates for .NET Framework version 1.0, which is included in these editions. However, it does not include update rollups for the Windows Media Center application in Windows XP MCE 2005.[82] SP3 also omits security updates for Windows Media Player 10, although the player is included in Windows XP MCE 2005.[82] The Address Bar DeskBand on the Taskbar is no longer included due to legal restrictions.[83]

^1 Even though this is Microsoft's stated minimum processor speed for Windows XP, it is possible to install and run the operating system on early IA-32 processors such as a P5Pentium without MMX instructions. Windows XP is not compatible with processors older than Pentium (such as 486) because it requires CMPXCHG8B instructions.[92]

^2 A Microsoft TechNet paper from Summer 2001 (before Windows XP's actual release), states that: "A computer with 64 MB of RAM will have sufficient resources to run Windows XP and a few applications with moderate memory requirements." (Emphasis added.) These were said to be office productivity applications, e-mail programs, and web browsers (of the time). With such a configuration, user interface enhancements and fast user switching are turned off by default. For comparable workloads, 64 MB of RAM was then regarded as providing an equal or better user experience on Windows XP with similar settings than it would with Windows ME on the same hardware. In a later section of the paper, superior performance over Windows ME was noted with 128 MB of RAM or more, and with computers that exceed the minimum hardware requirements.[93]

Windows XP Professional supports up to two physical processors[97] (CPU sockets);[98] Windows XP Home Edition is limited to one.[99]

Windows XP supports a greater number of logical processors. A logical processor is either: 1) One of the two handlers of threads of instructions in one of the cores of a physical processor with support for hyper-threading present and enabled; or 2) one of the cores of one of the physical processors without enabled support for hyper-threading. Windows XP 32-bit editions support up to 32 logical processors;[100] 64-bit editions support up to 64 logical processors.[101]

Mainstream support ended on April 8, 2014.
Extended support ends on April, 2019.[104]

Support for Windows XP without a service pack ended on September 30, 2005.[4] Windows XP Service Pack 1 and 1a were retired on October 10, 2006,[4] and Windows XP Service Pack 2 reached end of support on July 13, 2010, almost six years after its general availability.[4] The company stopped general licensing of Windows XP to OEMs and terminated retail sales of the operating system on June 30, 2008, 17 months after the release of Windows Vista.[105][106] However, an exception was announced on April 3, 2008, for OEMs producing what it defined as "ultra low-cost personal computers", particularly netbooks, until one year after the availability of Windows 7 (October 22, 2010). Analysts felt that the move was primarily intended to combat the threat of Linux-based netbooks, although Microsoft's Kevin Hutz stated that the decision was due to apparent market demand for low-end computers with Windows.[107][108][109]

On April 14, 2009, Windows XP exited mainstream support and entered the Extended Support phase; Microsoft continued to provide security updates every month for Windows XP; however, free technical support, warranty claims, and design changes were no longer being offered. Extended support ended on April 8, 2014, over 12 years since the release of XP; normally Microsoft products have a support life cycle of only 10 years.[111] Beyond the final security updates released on April 8, no more security patches or support information are provided for XP free-of-charge; "critical patches" will still be created, and made available only to customers subscribing to a paid "Custom Support" plan.[111][112][113] As it is a Windows component, all versions of Internet Explorer for Windows XP also became unsupported.[114]

Microsoft will continue to provide Security Essentialsvirus definitions and updates for its Malicious Software Removal Tool (MSRT) for XP until July 14, 2015.[115] As the end of extended support approached, Microsoft began to increasingly urge XP customers to migrate to newer versions such as Windows 7 or 8 in the interest of security, suggesting that attackers could reverse engineer security patches for newer versions of Windows and use them to target equivalent vulnerabilities in XP.[116][117][118] On March 8, 2014, Microsoft deployed an update for XP that, on the 8th of each month, displays a pop-up notification to remind users about the end of support—these notifications may be disabled by the user.[119] Microsoft also partnered with Laplink to provide a special "express" version of its PCmover software to help users migrate files and settings from XP to a computer with a newer version of Windows.[119][120]

Despite the approaching end of support, there have still been notable holdouts who have not migrated past XP; many users elected to remain on XP because of the poor reception of Windows Vista, sales of newer PCs with newer versions of Windows declined due to the Great Recession and the effects of Vista, and deployments of new versions of Windows in enterprise environments require a large amount of planning, which includes testing applications for compatibility (especially those that are dependent on Internet Explorer 6, which is not compatible with newer versions of Windows).[121][122][123][124] Major security software vendors (including Microsoft itself) plan to continue offering support and definitions for Windows XP past the end of support to varying extents, along with the developers of Google Chrome, Mozilla Firefox, and Opera web browsers;[114] despite these measures, critics similarly argued that users should eventually migrate from XP to a supported platform.[121][123][125][126][127]

As of January 2014, at least 49% of all computers in China still ran XP. These holdouts have been influenced by several factors; prices of genuine copies of Windows in the country are high, while Ni Guangnan of the Chinese Academy of Sciences warned that Windows 8 could allegedly expose users to surveillance by the United States government, and the Chinese government would ban the purchase of Windows 8 products for government use in May 2014 in protest of Microsoft's inability to provide "guaranteed" support. The government also had concerns that the impending end of support could affect their anti-piracy initiatives with Microsoft, as users would simply pirate newer versions rather than purchasing them legally. As such, government officials formally requested that Microsoft extend the support period for XP for these reasons. While Microsoft did not comply with their requests, a number of major Chinese software developers, such as Lenovo, Kingsoft and Tencent, will provide free support and resources for Chinese users migrating from XP.[123][128][129][130][131] Several governments, in particular the Netherlands and the United Kingdom, elected to negotiate "Custom Support" plans with Microsoft for their continued, internal use of Windows XP; the British government's deal lasts for a year, also covers support for Office 2003 (which reached end-of-life the same day) and cost £5.5 million.[127][132][133]

In January 2014, it was estimated that more than 95% of the 3 million automated teller machines in the world were still running Windows XP (which largely replaced IBM's OS/2 as the predominant operating system on ATMs); ATMs have an average lifecycle of between seven and ten years, but some have had lifecycles as long as 15. Plans were being made by several ATM vendors and their customers to migrate to Windows 7-based systems over the course of 2014, while vendors have also considered the possibility of using Linux-based platforms in the future to give them more flexibility for support lifecycles. However, ATMs typically run the embedded variant of Windows XP, which is supported through January 2016.[134][135] Similarly specialized devices that run XP, particularly medical devices, must have any revisions to their software—even security updates for the underlying operating system—approved by relevant regulators before they can be released. For the same reason, manufacturers of medical devices had historically refused to provide, or even allow the installation of any Windows updates for these devices, leaving them open to security exploits and malware.[133][136]

On May 1, 2014, despite the end of support for the operating system, Microsoft released an emergency patch to correct a major, recently discovered security exploit in the Internet Explorer browser on all versions of Windows (including Windows XP).[137][138]

On release, Windows XP received mostly positive reviews. CNET described the operating system as being "worth the hype", considering the new interface to be "spiffier" and more intuitive than previous versions, but feeling that it may "annoy" experienced users with its "hand-holding". XP's expanded multimedia support and CD burning functionality was also noted, along with its streamlined networking tools. The performance improvements of XP in comparison to 2000 and ME were also praised, along with its increased number of built-in device drivers in comparison to 2000. The software compatibility tools were also praised, although it was noted that some programs, particularly older MS-DOS software, may not work correctly on XP due to its differing architecture. They panned Windows XP's new licensing model and product activation system, considering it to be a "slightly annoying roadblock", but acknowledged Microsoft's intent for the changes.[139]PC Magazine provided similar praise, although noting that a number of its online features were designed to promote Microsoft-owned services, and that aside from quicker boot times, XP's overall performance showed little difference over Windows 2000.[140]

According to web analytics data generated by Net Applications, Windows XP was the most widely used operating system until August 2012, when Windows 7 overtook it.[141] In January 2014, Net Applications reported a market share of 29.23% for XP, while W3Schools reported a share of 11.0%.[142][143]

According to web analytics data generated by StatOwl, Windows XP had a 27.82% market share as of November 2012, having dropped to second place in October 2011.[144]

According to web analytics data generated by W3Schools, from September 2003 to July 2011, Windows XP was the most widely used operating system for accessing the w3schools website, which they claim is consistent with statistics from other websites. As of May 2014[update], Windows XP market share was at 7.3% after having peaked at 76.1% in January 2007.[143]

According to Net Applications, Windows XP market share was 17.18% as of October 2014.[145]

According to Net Applications, as per the gathered statistics of February 2015, Windows XP holds 19.15% of the market share. [146]

^Schofield, Jack (November 13, 2001). "A very good job...?". The Guardian (London: Guardian Media Group). Retrieved June 30, 2011. The consensus feeling seems to be that XP provides the ease of use of Acorn and Apple systems, plus the solidity and advanced capabilities of Unix, while retaining most of the compatibility of Windows 95/98 and Me.